1. Field of the Invention
The present invention relates to miniaturized apparatus for conveying small quantities of liquid and particularly to fluid filling devices and miniaturized electrodes. More specifically, this invention is directed to techniques for conveying minute quantities of liquids and especially for techniques for filling small capillary tube micropipettes and other tiny chambers or vessels with a liquid. Accordingly, the general objects of the present invention are to provide novel and improved devices and methods of such character.
2. Description of the Prior Art
While not limited thereto in its utility, as will become apparent from the discussion below, the present invention is particularly useful in the filling of small capillary tube micropipettes and other small volume chambers or vessels that are normally difficult to fill completely with fluid because of narrow, deep or convoluted fluid passageways. Micropipettes, usually fabricated from glass and having microscopically small tips, find widespread usage in biological and chemical research for injecting fluid material into living cells and organelles in order, for example, to permit measurement of the electrical properties of such cells. Micropipettes are also employed to deliver minute amounts of fluid for microchemical analysis. The filling of micropipettes with the fluid material to be injected without the inclusion of air bubbles and dust particles is a problem of long standing in the art. The clogging of the micropipette tip by particles present in the injecting solution is one of the major causes of failure in microinjection experiments.
The technique for filling micropipettes most commonly employed prior to the present invention involves the use of a long, stainless steel hypodermic needle. However, the KCl solution used in the filling process can corrode and plug such stainless steel needles within a few days if the needle is not thoroughly cleaned after each use. Further, for micropipettes which are used in the study of ion channels, e.g., patch pipettes, the use of a metallic needle to fill the micropipette may have the undesirable result of introduction of metal ions into the filling solution. It is also to be noted that, when a metal needle is filled with a solution containing EDTA or EGTA, the solution can become very acidic within several minutes because EDTA chelates metal ions from the needle and therefore releases protons into the solution.
To summarize, there has been a long standing need in the art for a method of and apparatus for filling micropipettes easily and reliably. A filling technique and apparatus which meets the requirements of the art must eliminate air bubble formation and clogging due to the washing down of dust particles. The filling apparatus must also be nonmetallic, be reasonably durable and be sufficiently stiff to not bend significantly under its own weight while at the same time having enough flexibility to insure against easy fracture.
Filling apparatus in accordance with the present invention also has utility as a microelectrode and particularly an ion selective microelectrode. Such electrodes contain a liquid electrolyte selected as a function of the intended application. The same problems associated with the filling of micropipettes, as discussed above, are encountered when attempting to fill a microelectrode with an electrolyte. These problems have previously not been solved in a manner which is conducive to the efficient production of microelectrodes having a long service life.